This invention relates to a prime mover, an apparatus and method for extracting power from moving water such as tidal flows and river currents.
Hitherto, this has generally been proposed or achieved by means of turbines analogous to underwater windmills. The blades of these windmills rotate as a result of the water flow about a horizontal or vertical axis at low speeds of the order of 10 to 30 revolutions per minute and at high torque. Gearboxes are required to transfer rotation at such speeds to the high speeds required for electrical generators. The gearboxes are large, complex and expensive with high power losses. The gearboxes also suffer from reliability problems and are difficult to maintain, particularly when located under water.
GB1604372 discloses a device for utilising tidal energy which comprises two cylindrical tank members fitting slidably inside one another. The device is supported on a tripod resting on the seabed. A flotation collar renders the outer tank buoyant so that it rises and falls with the water level as a result of which air within the tanks is compressed by their relative movement. Connections provided in the cover of the inner tank allow the compressed air to be used to drive an air turbine situated at a remote location.
The current invention aims to provide a prime mover (for converting natural energy into mechanical power), an apparatus and a method for transferring kinetic energy from slow moving water. The prime mover can be used with any suitable energy removal scheme. For example it can be used to produce electrical energy directly or to provide a useful form of mechanical movement. In a further aspect of the invention, kinetic energy from slow moving water is transferred into kinetic energy of a fluid travelling at high speed. Preferably the fluid is air.
According to a first aspect of the invention there is provided a prime mover for extracting power from moving water comprising a body which is caused to oscillate relative to the water by reversing the direction of thrust generated by at least one submerged control member protruding from a side of the body.
Whilst this prime mover is ideally suited for extracting energy from flowing water, extraction from other flowing fluids is possible and the term xe2x80x9cwaterxe2x80x9d should be interpreted as covering other flowing liquids and gases throughout this document.
Preferably, at least one control member protrudes from each side of the body.
Preferably, the shape of the body is such that water is caused to travel faster over a portion of the surface of the body and in which one or more protruding control members are positioned at that portion of the surface of the body.
Preferably, the body comprises curved sides which orientate the body with respect to a flow of water so that the control member or members are substantially perpendicular to the direction of flow of the moving water.
Preferably, the control member(s) is generally planar.
Preferably, the shape of the sides is symmetrical.
Preferably, the sides of the body are convex.
Preferably, at least one second protruding control member is provided fixed with respect to the body and arranged so that when the direction of thrust of a first reversible protruding control member is reversed, the angle of the second fixed control member with respect to the flow of water is altered so that the action of the water on that second fixed member. Thus the control member acts like a tail plane of an aircraft.
Preferably, the fixed second control member is positioned at a point on the body at which the velocity of the water flowing past the body is at or near a maximum.
Preferably, the first reversible control member is spaced laterally from it in the direction of the water flow. Preferably, the reversible control member is downstream of the fixed control member. This is much like a tail plane on an aircraft.
Preferably, one or more control members comprise hydroplanes whereby the direction of thrust is reversed by reversing the angle of inclination of at least one hydroplane.
Preferably, the distribution of control members on opposing sides of the body is symmetrical.
Preferably, the body is elongate and tends to orientate itself so that it is elongate in the direction of flow of the current.
Preferably, the body oscillates in a vertical direction.
Preferably, one or more reversible controls members are pivotable in its entirety.
Preferably, one or more reversible control member are pivotable about an edge protruding from the body.
Preferably, one or more reversible control members are pivotable about a central axis protruding from the body.
Preferably, one or more of the reversible control members are formed by a pivotable flap mounted to a control member or other mounting means fixed with respect to the body.
Preferably, one or more reversible control members have an aerofoil shape.
In a further embodiment, one or more control members comprise a rotatable cylindrical structure whose direction of rotation can be reversed to generate a change in direction of thrust. As an example, the cylindrical structure may form a continuous cylinder or may have spaced vanes.
Preferably, more than one control member is provided on opposing sides of the body.
Preferably, the control members are spaced along the body in a direction substantially perpendicular to the direction of flow of the water when the body is orientated so that its control members protrude from the body in a direction substantially perpendicular to the direction of flow of water.
Preferably, the body is arranged to oscillate vertically and two or more control members are provided on opposing sides of the body spaced in a substantially vertical line.
Preferably, three or more control members are provided on each side and the separation of the control members is substantially equal.
According to a further aspect there is provided, apparatus for extracting power from moving water comprising a prime mover as described herein.
Preferably, the prime mover is connected to mooring means secured or securable under water.
Preferably, the prime mover is connected to mooring cable.
Preferably, the prime mover is axially slidably mounted or mountable to a column secured or securable under water in an upright position.
Preferably, the prime mover comprises a downwardly extending tube which surrounds the column.
Preferably, power conversion means are provided for converting the oscillations of the prime mover into another form of power such as electrical power.
Preferably, the prime mover is submerged when generating power.
Preferably, power conversion means are provided comprising one or more hydraulic pumps, a crank for generating mechanical rotation or means for generating electricity such as an electric coil and magnet.
Preferably, power conversion means are provided comprising a fluid pump for pumping fluid to a higher level.
Preferably, the apparatus is moored to or mounted on a structure such as column on which apparatus for extracting power from wind or wave is mounted. Thus, the prime mover extracts power from tidal or river current flow, and power is also extracted from wind or waves. Whilst the prime mover is ideally suited to extracting power from tidal and river currents, it is also adaptable to be used for extracting power from waves as will be explained below in connection with a preferred embodiment.
Preferably, the prime mover is buoyant. Typically, it will float on the surface with part of its structure below the surface.
Preferably, the prime mover comprises an open bottomed tank which when it oscillates alternately compresses and decompresses a fluid inside it between a closed top of the tank and the water surface.
It will be understood by those skilled in the art from the information disclosed herein that the inventions in this preferred embodiment can operate in two modes.
In the first mode, power is extracted from tidal and river flows in the following way. As water flows past the control member, upward and downward thrust is produced causing the prime mover to move in a plane which crosses the flow direction (typically it is roughly perpendicular). Reversing the control member causes the direction of thrust to be reversed and when this is repeated the prime mover reciprocates generally in the plane.
This reciprocating movement can be converted into a more useful form of energy by an appropriate energy removal arrangement. In this preferred embodiment the prime mover is a tank which alternately compresses and decompresses a fluid.
In the second mode, power is extracted from waves. As waves impinge on the tank, the water level inside it rises and falls relative to the top of the collector. Vertical movement of the tank is damped by the drag of the hydroplanes. This drag can be supplemented, though this is not always necessary, by reversing the control member or members to produce thrust in a direction opposite to the rise and fall of water in the waves. Thus the tank tends to remain stationary relative to a fixed point, the shore or sea bed say, but the fluid inside the tank is alternately compressed and decompressed by the action of the waves.
Preferably, at least one duct in the top of the tank permits the fluid alternately to flow out of and into the tank.
Preferably, the fluid flowing through one or more ducts drives a turbine. Preferably, the turbine is mounted on the tank. Thus, the turbine operates in air when the fluid chosen is air. Preferably, the turbine is directly drivably connected to an electrical generator.
Preferably, the number and/or size of ducts open at any time, or selected to drive a selected turbine at a particular time, can be varied so that the flow of air can be optimized to the efficiency requirements of the turbine.
Preferably, a turbine is housed in a duct. Preferably, a generator, or combined turbine and generator is housed in the duct.
Preferably, the turbine rotates in the same direction irrespective of the flow of fluid out of or into the tank.
Preferably, valve means are provided so that fluid passes through the turbine in the same direction irrespective of the flow of fluid out of or into the tank.
Preferably, the fluid is air.
In a further aspect there is provided a method of extracting power from moving water comprising repeatedly reversing the direction of thrust generated by a submerged control member protruding from a body in a prime mover as described herein.